A problem which is the subject of increasing attention at the present time is the environmentally sound disposal of waste materials such as materials resulting from various industrial and technical procedures. One such material is fluidised bed ash which is produced in large quantities in the combustion of fuels which preferably have a high content of ballast or inerts, more especially coal, in a fluidised bed firing process. In order to bind the sulfur present in the fuels, calcium oxide or calcium carbonate is added to the firing chamber, with the result that the ash produced includes inter alia a comparatively high proportion of anhydrous calcium sulfate (10-10%). Further reference is made to this below.
The use of fluidised bed ash for the production of additive materials, for example for lightweight concrete or dry building plates and panels is referred to in German laid-open application (De-OS) No 38 08 519. In that procedure the fluidised bed ash upon being discharged from the firing installation is treated inter alia with a binding agent such as cement, lime or gypsum. German laid-open application (De-OS) No 33 24 708 discloses the use of fluidised bed ash in building materials for underground working or mining, for example for building dams or embankments, columns or piers.
German laid-open application (DE-OS) No 37 26 903 refers to the use of blast furnace slag as a hydraulic binding agent for the production of a liquefied floor finishing mortar. As the chemical composition of blast furnace slag is not comparable to the ash which is produced in a fluidised bed firing process, and that applies in particular in regard to the content of anhydrous calcium sulfate, the results obtained in relation to such a floor material cannot be applied to mortar based on a different binding agent.
German published specification (DE-AS) No 10 77 130 discloses the use of crushed slag as an additive for a floor mortar on an anhydrite basis. However, no information is contained therein about the origin or composition of the slag.
A special modification of anhydrous calcium sulfate, as referred to above in connection with the composition of fluidised bed ash, is the calcium sulfate contained in the anhydrite binder in accordance with German standard DIN 4208 (March 1984). That modification, which is referred to for the sake of simplicity hereinafter as `anhydrite`, is made into a binder material (DIN 4208) by the addition of what can be referred to as activators, for example builder's lime or potassium sulfate, and that material, by the addition of sand and water, can be made into a mortar for the production of finished floors (see German standard DIN 18353, August 1974). The material properties required in that respect from the hardened floor, such as flexural tensile strength, are set forth in German standard DIN 18560, part 2.
For the production of such an anhydrite plaster use is made of anhydrites which come from natural deposits, being therefore referred to as natural anhydrite, or anhydrites which occur in a chemical working operation, for example in the production of hydrofluoric acid from fluorite, referred to as synthetic anhydrite.